The invention relates to a continuously operating press for pressing planar products. In particular, the press is suited for use in the production of laminated wood products such as beams of the so-called laminated veneer lumber type (LVL beam) made by adhering to each other a layout of parallel strands of wood. In these presses, the product is passed under pressure directed thereon by two facing press means forming a press gap. During the pressing step, generally also heat is imposed on the product in order to promote the curing of the glue applied to the product layup.
Continuous presses of this type used in the art are generally implemented using a construction wherein the product to be pressed is passed into a gap formed between two opposed metal belts arranged to run continuously in endless loops, both of which having in one portion of their run adapted a compressing section in which the faces of the product are subjected to a compressing pressure. The compressing pressure is applied by means of platens adapted to operate in the interior of the belt loops. Between the platen and the press belt are placed metallic rod-like rollers running under a control, and transmitting the compressing pressure from the platens to the press belt and, if so desired, also heat from heatable platens. This kind of construction subjects the press belt to lineal forces that impose local stresses on both the belt and the rollers loading the same. Further, the press belt must exhibit a given degree of stiffness so that the compressing pressure will extend also to the marginal areas of the belt not covered by the lineal contact of the rollers. The construction is also limited as to its heat transfer capability that in practice is curtailed to conductive heat transmission via the rollers.
The press construction according to the invention makes now possible to impose the compressing pressure on the product in a substantially uniform fashion over the entire surface of the product while simultaneously the compressing force is distributed substantially equally over the belt surface. Resultingly, the strength specifications of the belt used in the press are relaxed as compared with the prior art. Hence, the press belt may be replaced with an element of a material different from a metallic belt. Also the efficiency of thermal transmission between the press platens and the product can be improved. In certain applications it is even possible to omit the belt entirely from the press construction.
The invention is implemented in a continuously operating press comprising facing platens between which the product to be pressed is passed in order to subject the same to compression, the press is provided with slats introduced as a continuous line of adjacent slat elements between the product being pressed and both ones of the press platens so as to make the slats to travel with the product being pressed and to slide along the press platens, whereby the surface of the slats facing the platens is provided with a tray recess, at least one of the press platens is provided with pressurized-medium ducts whose mutual duct-to-duct spacing between their exit openings in the operating direction of the press is greater than the summed width dimension in the press operating direction across the tray recess boundary ridge areas of two successive slats, but yet is smaller than the edge-to-edge internal width of a single tray recess in the same operating direction, and further that each duct communicates with a pressurized-medium source different from that supplying the duct located immediately preceding or, respectively, following said duct in the operating direction of the press. Other characterizing features of the invention will be evident from the dependent claims appended to this application.